Add entry_tag to leverage callback

closes #6929

freqtrade/templates/subtemplates/strategy_methods_advanced.j2

@@ -267,8 +267,8 @@ def adjust_trade_position(self, trade: 'Trade', current_time: 'datetime',
     return None
 
 def leverage(self, pair: str, current_time: datetime, current_rate: float,
-                proposed_leverage: float, max_leverage: float, side: str,
-                **kwargs) -> float:
+             proposed_leverage: float, max_leverage: float, entry_tag: Optional[str],
+             side: str, **kwargs) -> float:
     """
     Customize leverage for each new trade. This method is only called in futures mode.
 
@@ -277,6 +277,7 @@ def leverage(self, pair: str, current_time: datetime, current_rate: float,
     :param current_rate: Rate, calculated based on pricing settings in exit_pricing.
     :param proposed_leverage: A leverage proposed by the bot.
     :param max_leverage: Max leverage allowed on this pair
+    :param entry_tag: Optional entry_tag (buy_tag) if provided with the buy signal.
     :param side: 'long' or 'short' - indicating the direction of the proposed trade
     :return: A leverage amount, which is between 1.0 and max_leverage.
     """